linux-kernel - Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page

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Message-ID: <YCt/N9LkJT1VJEW1@dhcp22.suse.cz>
Date:   Tue, 16 Feb 2021 09:15:51 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap
 pages associated with each HugeTLB page

On Tue 16-02-21 12:34:41, Muchun Song wrote:
> On Tue, Feb 16, 2021 at 3:39 AM Michal Hocko <mhocko@...e.com> wrote:
[...]
> > > Using GFP_KERNEL will also use the current task cpuset to allocate
> > > memory. Do we have an interface to ignore current task cpuset？If not,
> > > WQ may be the only option and it also will not limit the context of
> > > put_page. Right?
> >
> > Well, GFP_KERNEL is constrained to the task cpuset only if the said
> > cpuset is hardwalled IIRC. But I do not see why this is a problem.
> 
> I mean that if there are more than one node in the system,
> but the current task cpuset only allows one node.

How would that cpuset get a huge pages from a node which is not part of
the cpuset? Well, that would be possible if the cpuset was dynamic but I
am not sure that such a configuration would be very sensible along with
hardwall setup.

> If current
> node has no memory and other nodes have enough memory.
> We can fail to allocate vmemmap pages. But actually it is
> suitable to allocate vmemmap pages from other nodes.
> Right?

Falling back to a different node would be very suboptimal because then
you would have vmemmap back by remote pages. We do not want that.
-- 
Michal Hocko
SUSE Labs